This invention pertains to an overload indicating link usable as a serial element in a lifting line. More particularly, it pertains to a link that will telescope to a longer length when a linear slip clutch releases or a replaceable shear pin fails. As an option, a swivel function can be provided in the fuse housing. Arrangements for audible and visual indications of overload are disclosed.
It is commonplace in most load lifting systems to use slings and lines with less lifting capacity than the hoisting gear. If the load has been underestimated or is hung up on other masses, the light tackle involved often breaks with consequence that can be life threatening. The oil industry provides an example.
When the main hoist system of a drilling rig is used to lift small loads, lines and slings of modest capacity are connected to the load and to the traveling block. If the load gets hung, the traveling block of the massive draw works will part the lifting line and drop the load.
City construction cranes and helicopters often lift loads not fully visible at the time first lifting forces are applied.
There is a need for a warning system that will clearly indicate that an over-limit load has been encountered. A linkage with a linear slip clutch, or a breakable element, that will part and allow the load to move a few inches before being stopped by safety elements will generally shock the lifting system. The shock will alert control personnel and invite alternate load management actions. In high noise level areas, a visible overload indicator system is appropriate. In quiet areas where a sound producing overload signal can be heard, sound producing overload responsive gear is needed.
It is an object of this invention to provide a lifting line safety link that will respond to a load exceeding a preset limit by extending a predetermined amount but retain needed lifting ability at the extended length.
It is another object to provide means to restore the safety link to the original configuration with minimal effort.
It is still another object to provide a safety link that restores itself automatically when the load is reduced.
It is yet another object to provide visual or audible indications that the safety link has been overloaded.
There is a preferred embodiment for each of several load ranges, and for each likelihood of overload. When overload rarely occurs, it is appropriate to use shear pin failure as the initiating mechanism. If overload often occurs, especially in cases that are very dangerous or delays are expensive, the cost of linear clutches is justified. The principal structures for each can be quite similar, and they are provided.
The means to safely allow a telescoping body to extend having been established, the need to provide visual or sound indicators of overload arose. That need produced signal means that can be used selectively on the elected housings.
The preferred embodiment for use in limited equipment circumstances is a link, with lifting line attachment means at opposite ends and a telescoping body. A shear pin in a cross bore axially secures the telescoping body in the shortened configuration. When a preselected amount of load is applied to the ends of the body, the shear pin parts and the body telescopes to a longer length. The body has a travel limiting abutment to prevent separation of the body. An optional sleeve retains the shear pin before failure, and the severed shear pin ends after failure.
In the linear slip clutch version, members in an interference arrangement hold the telescoping body in the shortened state until load exceeding a preselected amount is experienced and causes resilient elements to distort to allow the interfering elements to pass. In these simple versions, the offending load is removed and the telescope is pushed back to the shortened state to restore the interfering situation between elements that prevent extension of the body. In the automatic re-setting version, bias means forces the body to telescope back to the shortened state when load is reduced to a selected amount.
On any of the housings involved, as indicated above, an optional wing-like indicator vane arrangement extends to signal operators above that overload has occurred. The vanes fold when the lengthened body is shortened again.
An option, usable alone or in combination with visual indications, provides a loud shriek when overload occurs. The preferred telescoping bodies, however secured in the shortened state, can function as piston and cylinder arrangements. When overload extension occurs, it represents considerable energy briefly available. The internal parts move fast relative to the body and define a variable volume enclosure. To allow air to be expelled from the suddenly shrinking variable volume enclosure, a whistle-type escape is provided. It is essentially a copy of the air passages of pressure can powered boat horns.
An alternate form of the invention provides a swivel as part of the telescoping body. The swivel performs the conventional function of a separate swivel usually used to allow the lifting line to twist, or unwind, without spinning the payload being lifted. It is also used in cases needing payload rotation not permitted by the hoist gear itself.
These and other objects, advantages, and features of this invention will be apparent to those skilled in the art from a consideration of this specification, including the attached claims and appended drawings.